FIG. 28 shows a finned tube-type heat exchanger according to the conventional technique. In a heat exchanger 1, a plurality of thin plate-shaped fins 3 are attached to a tube 2 for a fluid to flow therethrough. In general, a fluid having a high heat transfer coefficient (such as, for example, water, CO2, or a HCF-based refrigerant) is passed inside the tube 2, and a fluid having a low heat transfer coefficient (such as, for example, air) is passed outside the tube 2.
The fins 3 are arranged side by side in the extending direction of the tube 2, and heat exchange is performed between a fluid flowing through the tube 2 and a fluid supplied between the fins 3 as indicated by an arrow A1. On the outside of the tube 2, which has a low heat conductivity, the fins 3 increase a heat exchange area and thus allow a large heat exchange amount to be obtained. That is why a finned tube-type heat exchanger is in common use as a heat exchanger for performing heat exchange between gases and between a gas and a liquid.
The above-described finned tube-type heat exchanger 1 according to the conventional technique has presented a problem that, on a downstream side of the fins 3, a boundary layer of a flow in the vicinity of a surface of the fins 3 has an increased thickness, causing a decrease in heat transfer coefficient. In order to solve this problem, Patent Document 1 discloses a heat exchanger with fins having cut and raised portions. The cut and raised portions provided in the fins has a leading edge effect by which the thickness of a boundary layer of a flow in the vicinity of a surface of the fins can be decreased. This leads to a decrease in heat conductivity between the fins and a fluid and thus can improve heat exchange efficiency.